Harriers have had problems before when hovering - i'm not too sure on the correct term for it, but Harriers hover by turning their exhaust nozzels downwards. Now of course, being an exhaust of a jet engine, the temperature of the exhaust fumes/air is extremely hot.
Now, assuming that everyone has a rough knowledge of how a jet turbine works, what can happen is that the engine re-inducts this already hot air, causing some sort of compression lock in the engine, causing the engine to "stall".
As far as I knew this was more of a tendancy for long time low level hovering, but that may possibly be what happened in this case.
oh yeah also - http://news.bbc.co.uk/1/hi/england/2168921.stm